The present invention concerns a support element for mounting at least two wave-modifying elements and a corresponding production method.
The present invention further concerns an optical modifier, for example for coupling in and out signals of individual or a plurality of wavelength channels into or out of waveguides with such a support element.
The term wave-modifying element is used to denote any element which, placed in the beam path, influences one, a plurality of or even all wavelength channels of the optical channel. The term influence is used to denote for example reflecting, absorbing, amplifying, attenuating, interrupting or polarising.
It is usual in the meantime in particular in the telecommunication and data communication art for items of information to be transmitted optically, that is to say for example by way of optical waveguides. Optical waveguides are generally thin fibres comprising highly transparent optical materials which conduct light in the longitudinal direction thereof by multiple total reflection. The light which generally enters by way of a smooth entrance surface follows all the bends of the fibres and issues again at the end from an end surface which is generally also smooth. The electrical signals which are to be transmitted are converted after suitable modulation by an electrooptical transducer into light signals, generally in the infrared range, coupled into the optical waveguide, transmitted by the optical waveguide and converted back into electrical signals at the end by an optoelectrical transducer. In order to increase the transmission rate of the optical waveguides, it is in the meantime usual for a plurality of different communication signals to be transmitted simultaneously by way of an optical waveguide. For that purpose the communication signals are modulated. Respectively different carrier frequencies are used for the different communication signals, which frequencies are also referred to as channels. After transmission of the individual communication signals or wavelength channels by way of the optical waveguide the individual signals have to be separated and demodulated.
Therefore, devices for adding and selecting wavelength-encoded signals (light of a specific wavelength or specific wavelengths), so-called multiplexer or demultiplexer arrangements, are known in the art. Such devices use optical fibres which have a high level of information carrier density. The purpose of the devices is inter alia to separate from the plurality of transmitted items of information a corresponding item of information or a corresponding wavelength channel. For example narrow band mirrors are used for that separation procedure, which allow specific frequencies of the light to pass virtually unhindered while selected frequencies are reflected. When the light issues from the glass fibre however this inevitably involves beam spreading which has the result that either the intensity at the imaging point, that is to say at the point at which the filtered light is evaluated, is markedly reduced, or the use of suitable lens systems, for example gradient index lenses (GRIN lenses) is necessary in order to collimate the light on to the appropriate imaging point. As the embodiment with the lenses however suffers from the disadvantage that on the one hand they are fairly expensive and on the other hand require very accurate adjustment and in addition the imaging properties are also still wavelength-dependent, WO 02/21733 already proposed a coupling device having a curved reflecting surface. That coupling device serves for coupling signals for example into or out of glass fibres. The use of a reflecting surface makes it possible to forego the optical lens system as the beam spreading effect which inevitably occurs at the end of a glass fibre is at least partly compensated by the curved surface.
In the structure described in WO 02/21733 the wave-modifying elements are laid on both sides of a glass plate and possibly fixed thereon. That provides that the wave-modifying elements are arranged substantially on two mutually parallel planes so that a multiplexer-demultiplexer can be implemented by suitable positioning of the wave-modifying elements.
The use of the glass plate has the disadvantage however that the signal suffers from attenuation in the glass, that reflection phenomena can occur at the interfaces of the glass plate and that it is not possible to insert a further wave-modifying element between two wave-modifying elements which are mounted on opposite sides of the glass plate.
The structure with the glass plate further suffers from the disadvantage that the parallel surfaces of the glass plate are frequently not entirely in plane-parallel relationship with each other, which makes it necessary to effect expensive re-adjustment of the individual filters on the glass plate.